Because they are not living inside of me. Pregnancy is unlike any other event in the known universe. You cannot justify the killing of a human being living on the inside of the womb because we aren’t required to donate blood or organs to a human being living on the outside of the womb. A preborn child is exactly where they are supposed to be, doing exactly what they are supposed to be doing. I don’t understand why this is such a difficult concept.
By the way, the right to life does exist under the United States founding documents, to include the U.S. Constitution. We simply had seven men sitting on the Supreme Court decide that those rights don’t apply to preborn Americans, just like seven men once interpreted the protections of the Constitution to exclude African Americans. Killing the preborn is wrong, even if it’s legal. Just like slavery was wrong while it was legal.